1. Field of the Invention
The present invention relates to a receiving coil for magnetic resonance imaging (MRI), and particularly to a compatible technology of a receiving coil for MRI radio-frequency signals.
2. Description of the Prior Art
Currently an important research direction concerning the development of medical devices is the use of MRI-guided high intensity focused ultrasound (HIFU) equipment.
The new therapeutic method of combining MRI with HIFU allows a physician to locate a disease focus accurately via MRI and then apply high intensity focused ultrasonic waves to the disease focus for treatment, and at the same time the procedure is monitored in real-time by using MRI imaging. In the above-mentioned treatment, it is necessary to ensure the synchronization between the MRI imaging and the HIFU treatment so as to make the real-time MRI imaging possible.
However, currently available ordinary receiving coils for MRI radio-frequency signals are not compatible with HIFU, making it impossible for MRI and HIFU to work in a synchronized manner, thus it is impossible to use MRI real-time imaging in monitoring HIFU treatments.
Referring to FIGS. 1 and 2, the two figures show respectively the circuit principles and the logic principles of an ordinary receiving coil for MRI radio-frequency signals (referred to as an “ordinary coil” hereinbelow). An antenna 10 of the ordinary coil is used for receiving MRI radio-frequency signals (when the HIFU is turned on, it receives the MRI radio-frequency signals and the HIFU signals simultaneously), which are then supplied to an amplifier 11 located in a receiving channel after passing a matching circuit, so the received signals are connected into the MRI system after having been amplified. This matching circuit includes, in succession capacitors C10, C12 and C13 which are connected in parallel to the antenna 10, a capacitor C11 which is connected in series between the capacitors C10 and C12, and an inductor L10 which is connected in series between the capacitors C12 and C13.
Further referring to FIG. 5A, when the HIFU system is turned off and not working, this ordinary coil can receive MRI radio-frequency signals in a normal way, and the signals are supplied to the MRI system for normal imaging after having been amplified. However, when the HIFU is turned on, if it were attempted to use the MRI for real-time imaging at the same time so as to monitor the procedure of the HIFU treatment, the ordinary coil would be unable to operate normally, leading to the imaging results as shown in FIG. 5B. The reason responsible for the above-mentioned problem is that when the HIFU is operating, its output power is very high such that the signal intensity in the examination space is much higher than that of the MRI radio-frequency signals. Although the frequency of the HIFU signals is lower than that of the MRI radio-frequency signals, the fact that its signal intensity is extremely high causes the amplifier 11 connected to the antenna 10 to enter into a nonlinear operating state, so it is unable to proceed with the imaging normally. Therefore, it is unable to use the MRI real-time imaging in an MRI-guided HIFU during a HIFU treatment, and the therapy and monitoring have to be effected by operating the HIFU and MRI in an asynchronous manner, and obviously the need for real-time and accurate operation cannot be satisfied.